Specifications

115
Table 5.2.1-1: Summary of optimal Rsense value experiments. Green indicates
chosen value (success).
5.2.2 Verifying Gas Detection Mechanisms
In order to do simplistic verification of the gas detection hardware, the sensor
must first be connected as per schematics provided in the alcohol sensor section.
This may require connecting the regulators in the previous section; as such, it is
important to verify those before using them here, in order to prevent another
variable from being present in this verification routine.
After connecting the Alcohol sensor into the correct configuration, utilizing a 390
ohm load resistor, a measurement of voltage across this load resistor can be
taken to determine the voltage response of the fuel cell to a known quantity of
alcohol. Using a dry-gas that has been calibrated to a known BAC value, a
sample should be released into the alcohol sensor for a period of approximately
5 seconds. This will simulate the user’s interaction with the handheld
breathalyzer. After this interval has elapsed, a measurement of the voltage
should be recorded. Conducting this test repeatedly will result in a data set of
voltage responses over time that should be averaged, in order to determine an
average expected value of response based on a certain quantity of alcohol input.
This value can then be used to interpolate alcohol concentration at different
levels, based upon the set level of the calibration standard. Table 5.2.2-1 shows
the results of repeated testing of the alcohol sensor, using particular known
inputs.
Ideal
Charging
Condition
Current
Current Limiting
Resistor (ohm)
Input
Voltage
IC
Temperture
Fan
Stability
.94A
0.1
12.5V
47C
No
No
.94A
0.1
12.5V
38.2
Yes
Yes
.11A
0.4
12.5V
37C
No
Yes
.30A
0.3
12.5V
40C
No
Yes
.50A
0.2
12.5V
44C
No
No
.50A
0.2
15.1V
48C
No
No
.50A
0.2
15.1V
25.7C
Yes
Yes
.22A
0.4
15.1V
38.5C
No
Yes